Creaming rates

The creaming rate (defined as the proportion of the fat arriving in the cream layer per unit time) is proportional to the creaming parameter, H (Walstra and Oortwijn, 1975) ... 

This parameter shows a linear relationship with the creaming rate if the effect of aggregation of the globules is excluded (Riiegg and Blanc, 1981) it can be seen that larger globules in particular affect H, and thus the creaming rate. 

Cone, of Detergent xlO-4 m Coale- scence Rate Constant (Kc) Floccu- lation Rate Constant (Kf) Creaming Rate Constant (Per Cent/ Hour) Stability Factor (kT)... 

If we assume that the creaming rates are only significantly affected by hydrodynamic interactions, then the coefficients can be... 

Figure 3 shows the effect of increasing particle size on the relative rates of creaming and gravity-induced flocculation. As the particle size increases, the rate of flocculation increases faster than the creaming rate of the particles. This is a result which, at first, one wouldn t expect. According to Equations (4), (10), and (11), the total rate of particle loss due to creaming R is... 

Stokes s law. (1) The rate at which a spherical particle will rise or fall when suspended in a liquid medium varies as the square of its radius the density of the particle and the density and viscosity of the liquid are essential factors. Stokes s law is used in determining sedimentation of solids, creaming rate of fat particles in milk, etc. 

The rate of creaming and cream volume was measured using graduated cylinders. The creaming rate was assessed by comparing the cream volume with that of the maximum value obtained when the emulsion was stored at 55 C. The time tj j taken to reach a value of V /V = 0.3 (i.e., 30% of the maximum rate) was calculated [4]. 

Figure 21.8 shows the results for creaming rates obtained at various temperature, using a 20/80 O/W emulsion stabihsed with Synperonic PEF 127. It is clear from these data that 3 decreases with the increase in temperature. 

The former is directly proportional to the square of the droplet size according to the Stokes-Einstein expression. In spite of the broad droplet size distribution and the changing droplet size with time, measuring the creaming rate can still provide a useful method for determining the relative droplet sizes of different emulsion products. The ultimate emulsion stability is not solely controlled by... 

The smallest droplets (i.e., the slowest creaming rate) are produced for the mini-emulsion in the absence of polymer, and the droplet size increases slightly with increasing polymer content (in the range of 0-1 wt %). In addition, the mini-emulsion prepared by 1 % PSt and without CA phase separated very quickly, indicating that such a product is probably not stable toward diffusional degradation. 

Another emulsion shows undesirable creaming. To reduce creaming rate a small amount of a thickener, i.e., a polysaccharide, is added. However, it increases the creaming rate. How ... 

FIGURE 13.12 Creaming rate relative to the Stokes velocity v/vs of O-W emulsions of various volume fraction (p and of average droplet size under gravity ( ) or in a centrifuge (O)- (Results from the author s laboratory.)... 

Creaming or sedimentation of emulsions with dro plet sizes above 1 pm eauses some experimental diffr culty because of the ehange in the total amount of spins in the NMR-aetive volume of the sample tube diuing the experiment. This can be accounted for by extra reference measurements with no gradient applied before and after each NMR scan at a particular value of 5. In addition, such reference measurements may provide information on the creaming rate which is a useful characteristic of emulsions. 

Emulsions are thermodynamically unstable systems and will, as a function of time, separate to minimize the interfacial area between the oil phase and the water phase. If a density difference exists between the dispersed and continuous phases, dispersed droplets experience a vertical force in a gravitational field. The gravitational force is opposed by the fractional drag force and the buoyancy force. The resulting creaming rate vq of a single droplet is given by Stokes law ... 

The creaming profiles are presented as the deviation in specific conductivity as a function of time. Creaming rates were quantitatively determined by calculating the slope of the first linear part of the creaming profiles. 

Table SInitial Creaming Rates and Changes in Specific Conductivities in Kraft Lignin-Stabilized Emulsions...

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